Picture frame



FIG. 1 is a top, front perspective view of a picture frame showing our new design;

FIG. 2 is a bottom, rear perspective view thereof;

FIG. 3 is an enlarged cross-sectional view taken on line 3-3 of FIG. 1; and,

FIG. 4 is an enlarged cross-sectional view taken on line 4-4 of FIG. 1. 

The ornamental design for a picture frame, as shown. 